1. Field of the Invention
The invention relates to an optical fiber testing device that not only tests insertion loss and total return loss of fiber route, but also measures position and return of events.
2. Description of Related Art
A current way of detecting events on an optical fiber path is achieved using the so-called frequency modulated continuous wave (FMCW) technique. With reference to FIG. 4, the detection device using the FMCW principle mainly includes a laser emitter 80, a frequency modulated continuous signal generator 81, a directional coupler 82, a photo detector 83, a mixer 84, an amplifier 85, an analog/digital converter (ADC) 86, and a signal processing unit 87.
The laser emitter 80 can emit detecting light. The frequency modulated continuous signal generator 81 can generate a continuous cyclic FM signal. After the frequency modulated continuous signal and the detecting light are combined and then pass through the directional coupler 82, the signals are transmitted to an optical fiber network 100. When the frequency modulated continuous signal travels in the optical fiber network 100 and encounters a discontinuity interface, the frequency modulated continuous signal will be reflected in the optical fiber path.
The photo detector 83 receives the reflected frequency modulated continuous signal and converts it into an electrical signal. The mixer 84 mixes the original frequency modulated continuous signal (A) generated by the frequency-modulated continuous signal generator 81 and the frequency modulated continuous signal (B) reflected from the optical fiber network 100. The mixed waveform is shown in FIG. 5. A beat frequency is produced between the original frequency modulated continuous signal (A) and the reflected frequency modulated continuous signal (B).
The amplifier 85 amplifies the mixed frequency modulated continuous signals. The ADC 86 converts the amplified signals into digital signals, and transmits them to the signal processing unit 87. The signal processing unit 87 performs fast Fourier transform (FFT) on the digital signals to obtain a reflection frequency. The reflection frequency is then used to calculate the position of the reflection point, thereby obtaining all events existing on the optical fiber network 100. Taking the structure shown in FIG. 6 as an example, different events at different positions P to S are connected by an optical fiber network. Using the above-mentioned FMCW detection method, one obtains the trace shown in FIG. 7. The trace shows different event positions P, Q, R, S.
Although the trace of the event positions can be applied to effectively detect the exact position and return loss of each event on the optical fiber network 100. However, it does not tell the total return loss and insertion loss of the optical fiber network 100.